Ergot is the common name of a fungus in the genus Claviceps that is parasitic on certain grains and grasses. The fungus forms a sclerotium in winter, and this small structure is what is usually referred to as 'ergot', although referring to the members of the Claviceps genus as 'ergot' is also correct. There are about 50 known species of Claviceps, most of them in the tropical regions. Economically important species are Claviceps purpurea (parasitic on grasses and cereals), C. fusiformis (on pearl millet, buffel grass), C. paspali (on dallis grass), and C. africana[1](on sorghum). C. purpurea can affect a number of cereals including rye (its most common host), triticale, wheat and barley. It affects oats only rarely.

There are three races or varieties of C. purpurea, differing in their host specificity [2]:

Ergotism is the name for sometimes severe pathological syndromes affecting humans or animals that have ingested ergot alkaloid-containing plant material, such as ergot-contaminated grains. The common name for ergotism is "St. Anthony's fire", in reference to the symptoms, such as severe burning sensations in the limbs.[3] These are caused by effects of ergot alkaloids on the vascular system due to vasoconstriction of blood vessels, sometimes leading to gangrene and loss of limbs due to severely restricted blood circulation. The neurotropic activities of the ergot alkaloids may also cause hallucinations and attendant irrational behaviour, convulsions, and even death.[1][2] Other symptoms include strong uterine contractions, nausea, seizures, and unconsciousness. Historically, controlled doses of ergot were used to induce abortions and to stop maternal bleeding after childbirth. Ergot alkaloids are also used in products such as Cafergot (containing caffeine and ergotamine or ergoline) to treat migraine headaches. Simple ergot extract is no longer used as a pharmaceutical preparation.[How to reference and link to summary or text] Monks of the order of St. Anthony the Great specialized in treating ergotism victims with balms containing tranquilizing and circulation-stimulating plant extracts; they were also skilled in amputations.[How to reference and link to summary or text]

Linnda R. Caporael posited in 1976 that the hysterical symptoms of young women that had spurred the Salem witch trials had been the result of consuming ergot-tainted rye. [6] However, her conclusions were later disputed by Nicholas P. Spanos and Jack Gottlieb, after a review of the historical and medical evidence. [7] Other authors have likewise cast doubt on ergotism having been the cause of the Salem Witch Trials. [8]

The Great Fear in France during the Revolution has also been linked by some historians to the influence of ergot.

Poisonings due to consumption of seeds treated with mercury compounds are sometimes misidentified as ergotism, such as the case of mass-poisoning in the French village Pont-Saint-Esprit in 1951:

The mass poisoning which took place in the French town of Pont-St. Esprit in 1951 has been widely presented in the lay and scientific press as an example of ergotism. While the poisoning was traced to bread, ergotism was not the cause of the syndrome, which was due to a toxic mercury compound used to disinfect grain to be planted as seed. Some sacks of grain treated with the fungicide were inadvertently ground into flour and baked into bread. Albert Hofmann arrived at this conclusion after visiting Pont-St. Esprit, and analyzing samples of the bread (which contained no ergot alkaloids) and autopsy samples of four of the victims who succumbed (Hofmann 1980; Hofmann 1991). On the other hand, Swedish toxicologist Bo Holmstedt insists the poisoning was in fact due to ergotism (Holmstedt 1978).…[9]

As Dr. Simon Cotton (member of the Chemistry Department of Uppingham School, U.K.) notes, there have been numerous cases of mass-poisoning due to consumption of mercury-treated seeds:

More horrifying than this were epidemics of poisoning, caused by people eating treated seed grains. There was a serious epidemic in Iraq in 1956 and again in 1960, whilst use of seed wheat (which had been treated with a mixture of C2H5HgCl and C6H5HgOCOCH3) for food, caused the poisoning of about 100 people in West Pakistan in 1961. Another outbreak happened in Guatemala in 1965. Most serious was the disaster in Iraq in 1971–1972, when according to official figures 459 died. Grain had been treated with methyl mercury compounds as a fungicide and should have been planted. Instead it was sold for milling and made into bread. It had been dyed red as a warning and also had warning labels in English and Spanish that no one could understand.[10]